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Activated K-RAS increases polyamine uptake in human colon cancer cells through modulation of caveolar endocytosis

Upal K Basu Roy1, Nathaniel S Rial, Karen L Kachel

  • 1Biochemistry and Molecular and Cellular Biology Graduate Program, University of Arizona, Tucson, Arizona, USA.

Molecular Carcinogenesis
|January 8, 2008
PubMed

Insights

Colon cancer cells utilize a caveolar, non-clathrin pathway for polyamine uptake, regulated by caveolin-1 and K-RAS oncogene signaling.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Oncology

Background:

  • Endocytic pathways are crucial for cellular processes, including nutrient and molecule transport.
  • Specific mechanisms of polyamine uptake via endocytosis in mammalian cells remain largely undefined.
  • Polyamines are essential for cell growth and proliferation, and their dysregulation is linked to cancer.

Purpose of the Study:

  • To elucidate the specific endocytic mechanisms responsible for polyamine transport in colon cancer cells.
  • To investigate the role of dynamin, Eps15, caveolin-1, and K-RAS in polyamine uptake.
  • To understand how oncogenic K-RAS influences polyamine transport pathways.

Main Methods:

  • Utilized dominant-negative Dynamin and Eps15 to assess endocytic pathway involvement.
  • Performed sucrose density gradient ultracentrifugation to analyze polyamine co-sedimentation with membrane fractions.
  • Employed caveolin-1 knockdown and ectopic expression studies.
  • Investigated the impact of activated K-RAS oncogene on polyamine uptake and caveolin-1 phosphorylation.
  • Assessed the role of urokinase plasminogen activator (uPA) and SRC kinase inhibition.

Main Results:

  • Dominant-negative Dynamin, but not Eps15, inhibited polyamine uptake, suggesting a caveolar, non-clathrin route.
  • Polyamines co-fractionated with caveolin-1-rich lipid rafts.
  • Caveolin-1 knockdown increased, while its ectopic expression decreased, polyamine uptake.
  • Activated K-RAS significantly enhanced polyamine uptake via increased caveolin-1 phosphorylation at Y14.
  • K-RAS-induced caveolin-1 phosphorylation promotes caveolar endocytosis, further stimulated by uPA and abrogated by SRC inhibition.

Conclusions:

  • Polyamine transport in colon cancer cells occurs via a dynamin-dependent, clathrin-independent endocytic pathway.
  • This pathway is positively regulated by oncogenic K-RAS through caveolin-1 phosphorylation.
  • Caveolin-1 acts as a negative regulator of caveolar endocytosis, modulated by K-RAS signaling.

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